Intervulcanized elastomer blends

ABSTRACT

Intervulcanized compositions having improved curing efficiency are prepared by the free radical curing of a mixture of an ethylenically unsaturated diolefin polymer such as natural or synthetic rubber and a saturated or low unsaturation polymer such as an ethylene propylene elastomers copolymer which contains functional groups pendant to the polymer chain. These functional groups contain an olefinic or vinyl double bond positioned alpha, beta to a substituent group which activates the double bond towards free radical addition reactions with the diolefin polymer. Preferred functionality includes benzylic ester functionality represented by the structure: ##STR1## wherein R 2  and R 3  are independently selected from hydrogen or C 1  to C 6  alkyl, and R 4  is selected from hydrogen, C 1  to C 28  alkyl, aryl or C 2  to C 28  alkenyl.

This application is a divisional application of Ser. No. 08/305,547filed Sep. 14, 1994 now U.S. Pat. No. 5,473,017, which is acontinuation-in-part of application Ser. No. 08/129,292, filed Sep. 301993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the use of unsaturated derivatives ofsaturated or highly saturated elastomers as elastomer components in thepreparation of synergistically covulcanizable elastomer blendcompositions.

2. Description of Related Art

Vulcanizates based on blends of elastomers which contain little or noolefinic unsaturation with more highly unsaturated elastomers are ofinterest in the rubber industry primarily because of their specialproperties, e.g., superior resistance to ozone degradation andconsequent cracking, improved resistance to chemical attack, improvedtemperature stability and unique dynamic response. Examples of suchblends are those containing: (a) one or a mixture of low unsaturatedrubbers such as terpolymers of ethylene, propylene and up to about 10 wt% of a non-conjugated diene (EPDM), copolymers of a C₄ to C₇ isoolefin,e.g., isobutylene, with up to about 20 wt % isoprene (butyl rubber),halogenated butyl rubber and halogenated interpolymers of a C₅ to C₇isoolefin, e.g., isobutylene with up to about 20 wt % para-alkylstyrene,e.g., para-methylstyrene, mixed with: (b) one or more ethylenicallyunsaturated elastomers such as natural rubber, polybutadiene, copolymersof butadiene with styrene or acrylonitrile, and the like.

One of the problems associated with the curing of elastomer compositionscontaining such chemically diverse materials is the inability to achievea balanced cure of each individual component and also a trulyintervulcanized composition, i.e., a composition where predominantinterpolymer crosslinking takes place between different polymermolecules in the different phases. For example, in sulfur curablesystems containing a blend of highly unsaturated elastomer such asnatural rubber and a low unsaturation elastomer such as EPDM or butylrubber, the high unsaturation diene phase cures much faster than the lowunsaturation phase resulting in a highly cured polydiene phase and anundercured, curative starved low unsaturation phase, with little or nointerpolymer crosslinking taking place at the phase boundaries. As aconsequence of this lack of curing balance, the vulcanizates may exhibitinferior mechanical properties such as low tensile strength, lowmodulus, poor hysterisis and the like.

One technique used to minimize the problem of vulcanization imbalance isthe use of low or no unsaturation blend components which have beenmodified by the inclusion of functional groups in the polymer chainwhich functional groups are susceptible to crosslinking mechanismsindependent of the sulfur curing system used to crosslink the highlyunsaturated elastomer. For example, blends containing halogenated butylrubber or halogenated interpolymers of isobutylene andpara-methylstyrene can be vulcanized along with more highly unsaturatedrubbers by including an independent curing system for each type ofelastomer into the vulcanization recipe, e.g., a zinc oxide-based curingsystem which normally cures the halorubber and an accelerated sulfurcuring system which normally cures the highly unsaturated rubber.However, even in these systems there may be a drop-off of importantproperties of the cured composition such as modulus, tensile, elongationand the like in comparison to what can be calculated as thecomposition-based averaging of such properties based on the propertiesexhibited by each cured elastomer alone, i.e., the "tie line"properties. This drop-off in properties is most likely the result of thelack of ideal solubility (compatibility) of the different phases coupledwith the lack of significant interpolymer crosslinking.

It should be noted that the achievement of tie line or above tie linerheometer cure performance in curable elastomer blend systems is anunusual phenomenon and represents optimum cure performance. In mostsystems, rheometer torque increase for cured blends of differentelastomers will lie at least partially below the tie line which would begraphically depicted as a straight line over the blend range connectingthe rheometer torque increase values associated with each individualelastomer if cured alone. One blend system which allegedly achievesabove tie line performance is disclosed in Hopper et al., "OzoneResistant Blends", International Conference on Advances in theStabilization and Controlled Degradation of Polymers, Lucene,Switzerland, May 23-25, 1984. The publication discloses sulfur curableblends of modified EPDM rubber and a polydiene rubber such as natural orpolybutadiene rubber exhibiting blend torque increases which aregenerally slightly above tie line values. The modified EPDM employed isthe addition product of an N-chlorothio-N-methyl-p-toluene sulfonamideto elastomeric terpolymers of ethylene, propylene and a non-conjugateddiene such as 1,4-hexadiene or dicyclopentadiene.

SUMMARY OF THE INVENTION

The present invention is directed towards truly intervulcanizable blendscomprising a mixture of a diolefin polymer or copolymer and a saturatedor highly saturated elastomeric copolymer having a number averagemolecular weight of at least 10,000 and containing from about 0.01 up toabout 10 mole % of "Y" functional groups randomly distributed along andpendant to the elastomeric polymer chain, said Y functional groupscontaining an olefinic or vinyl double bond positioned alpha, beta to asubstituent group which activates said double bond towards free radicaladdition reactions. The preferred activating substituent groups arecarboxyl-containing groups, phosphoryl-containing groups,sulfonyl-containing groups, nitrile-containing groups, aromaticring-containing groups or a combination of such groups.

The present invention also provides for an intervulcanized compositionof a blend of elastomers, the blend comprising a diolefin polymer orcopolymer and a saturated or highly saturated polymer having covalentlybonded along the polymer backbone a group containing a free olefinic orvinyl double bond positioned alpha, beta to said_substituent group whichactivates the double bond for free radical addition reactions in thepresence of a free radical generator.

In a preferred embodiment, the elastomeric copolymer is a copolymer ofat least one C₂ -C₈ alpha-monoolefin with a non-conjugated diene or aparaalkylstyrene.

In another preferred embodiment, the pendant Y groups are ester groupsrepresented by the structure 1: ##STR2## wherein R₂ and R₃ areindependently selected from the group consisting of hydrogen and alkylcontaining 1 to about 6 carbon atoms, and R₄ is selected from the groupconsisting of hydrogen, an aryl group, e.g., phenyl, an alkyl groupcontaining from 1 to about 28 carbon atoms and an alkenyl groupcontaining from 2 to about 28 carbon atoms.

It has been found that the cure of compositions containing such blendsby ordinary curing mechanisms which generate free radicals in thediolefin polymer, e.g., accelerated sulfur cures, peroxide cures,radiation cures and the like, results not only in the individualcrosslinking of the blend components themselves but also crosslinkinginvolving the free radical generated in the diolefin polymer and thedouble bonds present pendant to the chain of the elastomeric copolymerwhich serve as free radical acceptors. Synergistic curing efficiency isreflected by rheometer torque increases that are consistently above thetie line values which might be expected based on the cure ofcompositions containing the individual elastomer components themselves.

Where the elastomeric copolymer is one containing no in-chainunsaturation, the resulting vulcanizate has enhanced ozone resistance,chemical resistance, high temperature stability and improved dynamicresponse. In particular, intervulcanized blends of this inventionexhibit improved modulus and tensile properties as compared withvulcanizates from blends of diolefin polymers and elastomeric copolymerswhich are devoid of the Y functional groups described above, morespecifically improved tensile strength, compression set and tension setproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of curing behavior as indicated by rheometer torquevalues vs. composition for blends containing natural rubber and amethacrylate modified terpolymer containing isobutylene andpara-methylstyrene, as well as blends of natural rubber and butylrubber.

FIG. 2 is also a plot of curing behavior for blends containingbutadiene/styrene copolymer rubber and different ester-modifiedisobutylene/para-methylstyrene copolymers.

FIG. 3 is a general graphic illustration plotting tie-line values andtorque increase values for elastomer blend compositions based on varyingcontent of blend components.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a curable composition based on a mixtureor blend of a functionalized elastomeric copolymer (a) and a differentdiolefin polymer or copolymer (b) characterized that when formulatedwith a curing system, e.g., a sulfur curing system or a peroxide curingsystem, and subjected to vulcanization conditions, the blend compositionexhibits a maximum rheometer torque increase ratio in accordance withthe formula:

    ΔM.sub.a+b /(ΔM.sub.a f.sub.a +ΔM.sub.b f.sub.b)

of greater than 1.25, preferably greater than 1.5 and more preferablygreater than 2.0, wherein:

ΔM_(a+b) =the torque increase observed for the blend of polymer (a) andpolymer (b);

ΔM_(a+b) =the torque increase observed for polymer (a) on its own;

f_(a+b) =the weight fraction of polymer (a) in the blend;

ΔM_(b) =the torque increase observed for polymer (b) on its own;

f_(b) =the weight fraction of polymer (b) in the blend.

The cure characteristic of torque increase (ΔM), also designated asM_(H) -M_(L), is evaluated using a Monsanto Rheometer at 3° arc inaccordance with ASTM procedure D-2084-71T. M_(L) represents minimum precure torque and M_(H) represents the highest torque achieved under cureconditions, e.g., at 160° C. and 60 minute cure time. The torqueincrease due to vulcanization is therefore the value of M_(H) minus thevalue of M_(L), (M_(H) -M_(L)) measured in pound-inches (lb.-in.).

The blend composition of the invention exhibits a synergistic curingeffect in the sense that the curing agent promotes intermolecularbonding between molecules of polymer (a) and polymer (b). FIG. 3illustrates conceptually the plot of rheometer torque increase versuscomposition for blends of the present invention. In particular, theblends of the present invention will show a plot similar to the curvedline DAE in FIG. 3. The points D and E, further identified with squares,represent the rheometer torque increases observed for polymers (a) and(b) on their own. The characteristic feature of the present inventionreflected in this plot is that for any blend (i.e., excluding the pointsD and E), the curved line DAE is consistently above the straight lineDBE. The straight line DBE is referred to as the "tie line" andrepresents the weighted average of the rheometer torque increases forthe individual polymers (a) and (b). Hitherto, tie line performance hasbeen regarded as the ultimate achievement in cocuring. However, itshould be noted that this can and often is achieved simply by optimizingthe individual intrapolymer cocuring of each of the polymers in theblend. The achievement of tie line performance does not imply theoccurrence of interpolymer cocuring. On the other hand, a rheometertorque increase plot that is consistently and significantly above thetie line, as in the curved line DAE in FIG. 1, is indicative ofeffective interpolymer cocuring.

It should be noted that the achievement of tie line performance is anunusual phenomenon and that for most systems the plot of rheometertorque increase versus composition will lie, at least partially, belowthe tie line. This point is illustrated by the comparative examples ofthe present invention.

The extent of interpolymer cocuring of a polymer blend may be measuredby the ratio AC/BC in FIG. 1. This ratio is a graphical depiction of themaximum rheometer torque increase ratio (ΔMa+b) described above. Fortypical compositions of the prior art, for which the observed plot isnot consistently above the tie line, this quantity is not convenientlymeasurable. For the few compositions of the prior art that achieve tieline performance, the value for this ratio is unity. For thecompositions of the present invention this ratio is greater than 1.25preferably greater than 1.5, most preferably greater than 2.0.

The elastomeric copolymer forming component (a) of the blends of thisinvention are copolymers of at least one C₂ to C₈ alpha monoolefin whichcontain little or no olefinic unsaturation along the polymer chain andwhich have been functionalized by reaction with functional reagentscontaining an olefinic or vinyl double bond positioned alpha, beta to asubstituent group which activates the double bond towards free radicaladdition reactions when contacted with a free radical source under freeradical generation conditions. These copolymers are thus able toparticipate in intercrosslinking reactions as free radical acceptors ofthe free radicals generated in the diolefin polymer (b) component of theblend under free radical curing conditions.

In addition to having the double bond as described above, the functionalreagent must contain a nucleophilic moiety (anion) which is reactivewith electrophilic groups present on the backbone of the elastomericcopolymer, e.g., halogen, hydroxy, and the like groups. The nucleophilicmoiety may be an anion derived from alcohol, phenol, carboxylic acid,thioalcohol, thiophenol, thiocarboxylic acid or imide, or a neutralnucleophile such as a tertiary amine. The double bond activating moietymay be a carbonyl containing group (e.g., COR, COOR, CONR₂, in which Ris alkyl or aryl), a phosphoryl or sulfonyl containing group [e.g.,PO(OR)₂ or SO₂ OR, in which R is alkyl or aryl], a nitrile-containinggroup or an aromatic ring-containing group, or a combination of suchgroups.

Exemplary of suitable reagents containing both double bond andnucleophilic functionality include the following: ##STR3##

Suitable anions include those derived by the reaction of bases, e.g.,tetraalkylammonium salts, with the compounds I to VII to remove theacidic hydrogen shown by "H". Included are acrylate (I) and methacrylate(II) anions, in which the carboxyl group serves as both nucleophile anddouble bond activator. In anions derived from compounds (III) and (IV)the carboxyl group serves as the nucleophile and as an activating groupeither by being situated directly on the double bond (III) or byextended conjugation with the double bond through the aromatic ring(IV). In both compounds (III) and (IV) and aromatic ring itself providesadditional activation of the double bond. In the anion derived fromcompound (V), the aromatic ring is the sole double bond activatingspecies and the nucleophile is a phenoxy anion. Anions derived from thecompounds monoethyl maleate (VI) or maleimide (VII) have double bondsactivated by two carbonyl containing groups and are suitable for thepresent invention. Thio analogs of anions derived from compounds (I) to(VI) are also suitable.

Suitable neutral nucleophilic reagents include tertiary amines such as4-dimethylaminostyrene (VIII). Additionally the sulfur analog of thecompound (V) may be sufficiently nucleophilic to be useful in thepresent invention without conversion to the corresponding anion.

Suitable reagents meeting the criteria set forth above includeunsaturated acids containing carbonyl functionality conjugated with thedouble bond such as acrylic acid methacrylic acid and the like; vinylaromatic reagents such as para-hydroxy styrene, para-alkoxy styrene and4-vinyl benzoic acid; unsaturated dicarboxylic acid derivatives such asmonoalkyl maleates and maleimide; and like reagents. Depending on thenature of the reagent nucleophile, these reagents can be made to reactwith electrophilic groups present in the backbone chain of theelastomeric copolymer to form ester, ether, amido or other linkages.

Examples of such nucleophilic substitution reactions with halogenatedcopolymers of isobutylene and para-methylstyrene are found in U.S. Pat.No. 5,162,445, the complete disclosure of which is incorporated hereinby reference.

The present invention will be more particularly described as it appliesto curable blends containing a benzylic ester-functionalized derivativeof a C₄ to C₇ isomonoolefin and a para-alkylstyrene as the elastomericcopolymer component of the blend. These materials may be prepared byreacting a halogenated copolymer of a C₄ to C₇ isoolefin, as describedbelow, with a nucleophilic reagent having the formula:

    (R.sub.3) (R.sub.4)C=C(R.sub.2)COO.sup.- M.sup.+,

wherein M is hydrogen, a metal ion or an onium ion and R₂, R₃ and R₄ areas described in Formula 1 above, under reaction conditions such that atleast a portion, and preferably substantially all, of the benzylichalide atoms present in the halogenated copolymer structure aredisplaced via a nucleophilic substitution reaction and replaced with thecorresponding ester group. In Formula 1 above, R₂ is preferably hydrogenor methyl, R₃ is preferably hydrogen and R₄ is preferably hydrogen or C₃to C₁₂ alkenyl.

The halogenated C₄ -C₇ isoolefin/para-alkylstyrene starting materialsare the halogenation product of random copolymers of a C₄ to C₇isoolefin, such as isobutylene, and a para-alkyl styrene comonomer,preferably para-methylstyrene containing at least about 80%, morepreferably at least about 90% by weight of the para isomer, and whereinat least some of the alkyl substituent groups present in the styrenemonomer units contain halogen. Preferred materials may be characterizedas isobutylene interpolymers containing the following monomer unitsrandomly spaced along the polymer chain: ##STR4## wherein R and R' areindependently hydrogen, lower alkyl, preferably C₁ to C₄ alkyl, and X isbromine or chlorine, and wherein the interpolymer is otherwisesubstantially free of ring halogen or halogen in the polymer backbonechain. Preferably R and R' are each hydrogen. Up to about 60 mole % ofthe para-alkylstyrene present in the interpolymer structure may be thehalogenated structure (2) above.

Most useful of such materials are elastomeric copolymers of isobutyleneand para-methylstyrene containing from about 0.5 to about 20 mole %para-methylstyrene wherein up to about 60 mole % of the methylsubstituent groups present on the benzyl ring contain a bromine orchlorine atom, preferably a bromine atom. These copolymers have asubstantially homogeneous compositional distribution such that at least95% by weight of the polymer has a para-alkylstyrene content within 10%of the average para-alkylstyrene content of the polymer. They are alsocharacterized by a very narrow molecular weight distribution (Mw/Mn) ofless than about 5, more preferably less than about 2.5, a preferredviscosity average molecular weight in the range of from about 300,000 upto about 2,000,000, and a preferred number average molecular weight inthe range of from about 25,000 to about 750,000, as determined by GelPermeation Chromatography.

The copolymers may be prepared by slurry polymerization of the monomermixture using a Lewis Acid catalyst, followed by halogenation,preferably bromination, in solution in the presence of halogen and aradical initiator such as heat and/or light and/or a chemical initiator.

Preferred brominated copolymers generally contain from about 0.1 toabout 5 mole % of bromomethyl groups, most of which is monobromomethyl,with less than 0.05 mole % dibromomethyl substituents present in thecopolymer. These copolymers, their method of preparation, their methodof cure and graft or functionalized polymers derived therefrom are moreparticularly disclosed in the above referenced U.S. Pat. No. 5,162,445.The acrylic and methacrylic ester functionalized derivatives of thesecopolymers are particularly disclosed in Examples 112 F-1 and 112 F-2 ofthis patent. Other functionalized derivatives, some of which are usefulin the present invention, are described in other portions of thispatent.

The nucleophilic substitution reaction described above is preferablyconducted in solution using a solvent system which will dissolve thehalogenated isoolefin/para-alkylstyrene copolymer and provide a solutionor dispersion of both the polymer and nucleophilic reagent so as toachieve intimate contact between the benzylic halogen of the basepolymer and the nucleophile. Suitable solvents include benzene, toluene,alkanes such as heptane, hexane, and cyclohexane and oxygen-containingsolvents or solvent mixtures such as tetrahydrofuran or mixtures thereofwith lower alcohols.

The reaction is preferably conducted under mild reaction conditions soas to avoid the formation of crosslinked or gelled products and minimizeunwanted side reactions. Preferred reaction temperatures range fromabout 20° to 100° C. The formation of the desired reaction product isfacilitated under mild reaction conditions by utilizing the onium saltof the nucleophilic agent as a reactant, i.e., the tetrabutyl ammoniumsalt.

Acids which may be used to form the ester nucleophile include thosewhich contain ethylenic or vinyl unsaturation conjugated with a carbonylgroup, e.g., acrylic acid, methacrylic acid, sorbic acid, cinnamic acidand the like, as well as mixtures thereof. The resulting reactionproduct may be characterized as a random interpolymer comprising atleast about 80 weight % of polymerized isoolefin containing 4 to 7carbon atoms and from about 0.05 up to about 20 weight % of aromaticmonomer units comprising a mixture of the following structure randomlydistributed therein: ##STR5## wherein R and R' are independentlyselected from the group consisting of hydrogen and C₁ to C₄ alkyl and Yis as defined in formula 1 above. Where all halogens present in thepolymer are completely displaced, the resulting product is a terpolymer;where the halogens are only partially displaced, the resulting productis a tetrapolymer which would also include some unreactedhalogen-containing monomer units as defined by monomer unit 2 above. Themore preferred materials are terpolymers containing at least about 95mole % of polymerized isobutylene and the balance a mixture ofpredominantly para-methylstyrene and less predominantly4-(acryloyloxy-methyl) styrene, 4-(methacryloyloxymethyl)methyl)styrene,4-(cinnamoyloxy-methyl) styrene or 4-cinnamoyloxy-methyl) styrene or4-(2,4-hexandienoyloxy-methyl) styrene.

Ester-functional elastomers which may be used as blend components in thepresent invention also include ester-modified elastomeric terpolymers ofethylene/propylene and up to about 10 wt % non-conjugated diene (EPDM)such as dicyclopentadiene, 1,4-hexadine, 5-methylene-2-norbornene and5-ethylidene-2-norbornene. The ester functionalized derivative of theseelastomers may be prepared by polymerizing ethylene, propylene and analcohol, e.g., a 5-norbornene-2-methanol derivative of thenon-conjugated diene under Zeigler-Natta polymerization conditions whichgive rise to alcohol functionalized derivative of the EPDM, as disclosedin U.S. Pat. No. 5,153,282, particularly Example 18, the completedisclosure of which patent is incorporated herein by reference.Conventional reaction of this product with the appropriate acid salt orchloride yields modified EPDM polymers containing the Y ester groups asdefined above attached to and pendant to the diene moiety of the polymerchain.

The diolefin polymer component with which the modified elastomericcomponent may be blended include high or low unsaturation polymers whichcontain conjugated or non-conjugated diene linkage. These includeelastomeric polymers such as polybutadiene, natural rubber, syntheticpolyisoprene, polychloroprene, copolymers of butadiene with up to about40 wt % of styrene or acrylonitrile, as well as relatively lowunsaturation diolefin polymers such as copolymers of ethylene, propyleneand up to 10 wt % of a non-conjugated diene such as norbornadiene,dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene,5-ethylidene-2-norbornene and the like, and copolymers of isobutyleneand up to 10 wt % of isoprene, and mixtures thereof. The diolefinpolymer may also be non-elastomeric and may include liquid to waxypolybutadiene or butadiene/acrylonitrile copolymers having a numberaverage molecular weight in the range of about 300 up to 10,000.Preferred diolefin polymers are polybutadiene, copolymers of butadienewith styrene or acrylonitrile, synthetic polyisoprene and naturalrubber.

The compositions may contain the elastomeric copolymer and diolefinpolymer components in a weight ratio in the range of from about 1:99 to99:1 each respectively, more preferably in the range of from about 10:90to 90:10 and most preferably from about 25:75 to 75:25.

As indicated above, the curing reaction is initiated by subjecting theblended mixture to curing conditions which will generate free radicalsand under conditions of mixing which will assure contact of theseactivated polymer chains with the polymer chains of the elastomericcopolymer containing the ester groups which serve as free radicalacceptors. This maximizes interpolymer crosslinking between thedifferent polymer chains as well as intrapolymez crosslinking within thechains of like polymers.

Suitable crosslinking methods include exposure to high energy radiation(ultra violet, electron-beam or gamma) or the inclusion of a suitableperoxide or accelerated sulfur vulcanizing system into the elastomerformulation.

Examples of suitable peroxides include organic peroxides such as dialkylperoxides, ketal peroxides, aralkyl peroxides, peroxyethers andperoxyesters. Preferred peroxides include di-cumylperoxide,di-tert-butylperoxide, benzoyl peroxide, tert-butylperbenzoate and likeknown free radical generators. The quantity of peroxide generally rangesfrom about 1 to about 10% by weight, preferably from about 1.5 to 6% byweight per hundred parts by weight of curable polymer present in thecomposition.

Accelerated sulfur vulcanization systems which may be used as curativesin the present invention include sulfur or mixtures of sulfur andsulfur-containing accelerators and/or phenol-formaldehyde resins.Suitable accelerators include benzothiazyl disulfide, N-oxydiethylenebenzothiazole-2-sulfenamide, 2-mercaptoben-zothiazole, alkyl phenoldisulfides, alkyl-thiuram sulfides, m-phenylenebismaleimide, N, N¹-diarylguanidines, dialkyl and diaryl-dithiocarbamates, and likematerials.

Suitable dialkyldithiocarbamates include the dialkyldithiocarbamates ofzinc, bismuth, cadium, copper, lead, selenium, and tellurium wherein thealkyl group contains from 1 to 5 carbon atoms, piperidiniumpentamethylenedithiocarbamate and mixtures thereof.

Suitable diarylthiocarbamates include the diaryldithiocarbamates ofzinc, bismuth, cadmium, copper, lead, selenium, tellurium, and mixturesthereof.

Suitable alkyl thiuram sulfides include dipentamethylene thiuramtetrasulfide, tetrabutylthiuram disulfide, tetraethylthiuram disulfide,tetramethylthiuram monosulfide, tetrabenzyl thiuram disulfide, andmixtures thereof.

Sulfur and vulcanization accelerators are normally added to thecomposition at levels in the range of from about 0.5 to about 8% byweight, based on the weight of elastomer present in the composition.

The accelerated sulfur curing system is preferably used as a cocurativein curing systems also containing zinc oxide or an equivalent thereof,as an auxiliary curative agent. Zinc oxide is normally used in suchsystems at a level of from about 0.2 to about 7 parts by weight per 100parts by weight of elastomer. The present invention provides forparticularly good low cure reversion where zinc oxide is present atlevels in the range of from about 0.5 to about 5.0 parts by weight per100 parts by weight of elastomer.

The elastomer polymer composition may also contain other additives suchas lubricants, fillers, plasticizers, tackifiers, coloring agents,blowing agents, and antioxidants.

Examples of fillers include inorganic fillers such as reinforcing gradecarbon black, silica, calcium carbonate, talc and clay, and organicfillers such as high-styrene resin, coumarone-indene resin, phenolicresin, lignin, modified melamine resins and petroleum resins.

Examples of lubricants include petroleum-type lubricants such as oils,paraffins, and liquid paraffins, coal tar-type lubricants such as coaltar and coal tar pitch; fatty oil-type lubricants such as castor oil,linseed oil, rapeseed oil and coconut oil; tall oil; waxes such asbeeswax, carnauba wax and lanolin; fatty acids and fatty acid salts suchas linoleic acid, palmitic acid, barium stearate, calcium stearate andzinc laureate; and synthetic polymeric substances such as petroleumresins.

Examples of plasticizers include hydrocarbon oils, e.g., paraffin,aromatic and napththenic oils, phthalic acid esters, adipic acid esters,sebacic acid esters and phosphoric acid-type plasticizers.

Examples of tackifiers are petroleum resins, coumarone-indene resins,terpene-phenol resins, and xylene/formaldehyde resins.

Examples of coloring agents are inorganic and organic pigments.

Examples of blowing agents are sodium bicarbonate, ammonium carbonate,N,N'-dinitrosopentamethylenetetramine, azocarbonamide,azobisisobutyronitrile, benzenesulfonyl hydrazide, toluenesulfonylhydrazide, calcium amide, p-toluenesulfonyl azide, salicyclic acid,phthalic acid and urea.

The vulcanizable composition may be prepared and blended using anysuitable mixing device such as an internal mixer (BrabenderPlasticorder), a Banbury Mixer, a mill mixer, a kneader or a similarmixing device. Blending temperatures and times may range from about 45°C. to 180° C. and 4 to 10 minutes respectively. After forming ahomogeneous mixture of the elastomers and optional fillers, processingaids, antioxidants and the like, the mixture is then vulcanized by thefurther mixing-in of crosslinking agents and accelerators followed byheating the resulting blend to a temperature of from about 100° to 200°C., more preferably from about 110° to 180° C. for a period of timeranging from about 1 to 60 minutes. It has been found thatintermolecular crosslinking is especially facilitated using a sulfursystem when the vulcanization temperature is maintained within the 120°C. to 160° C. range. Molded articles such as belts, tire components andhoses are prepared by shaping the prevulcanized formulation using anextruder or a mold, and subjecting the composition to temperatures andcuring times as set forth above.

The following examples are illustrative of the invention. The materialsused in the examples described below were as follows:

    ______________________________________                                        MA-IPMS     A copolymer of about 97.5 mole %                                              isobutylene, 1.7 mole % para-                                                 methylstyrene and 0.8 mole % of the 4-                                        (methacrylic acid-methyl) ester of                                            styrene, as prepared in Example A.                                SA-IPMS     A copolymer of about 97.5 mole %                                              isobutylene, 1.7 mole % para-                                                 methylstyrene and 0.8 mole % of the 4-                                        (sorbic acid-methyl) ester of styrene,                                        as prepared in Example B.                                         NR          Natural rubber (SMRL) having a Mooney                                         Viscosity ML(1 + 4) at 100° C. of 45-55.                   NATSYN 2200 A synthetic polyisoprene (PI) having a                                        Mooney Viscosity ML(1 + 4) at 100° C. of                               70-90.                                                            SBR 1502    A copolymer of butadiene and 23.5 wt % of                                     bound styrene having a Mooney Viscosity                                       ML(1 + 4) at 100° C. of 35.                                BUTYL 268   A copolymer of 98.5 mole % isobutylene                                        and 1.5 mole % isoprene having a Mooney                                       Viscosity ML(1 + 8) at 125° C. of 55.                      ZnO         Finely divided Zinc oxide.                                        TMTDS       Tetramethyl thiuram disulfide.                                    ETHYL ZIMATE                                                                              Zinc diethyldithiocarbamate.                                      ______________________________________                                    

EXAMPLE A

A methacryclic acid derivative of anisobutylene/para-methylstyrene/para-bromomethystyrene base terpolymer(MA-IPMS) was prepared as follows:

A 5000 mL glass-jacketed reaction vessel fitted with an overheadstirrer, a hose connector and a septum was purged with nitrogen. At roomtemperature under nitrogen, the vessel was charged with toluene (3100mL) and 475 g of the baseisobutylene/para-methylstyrene/para-bromomethylstyrene terpolymercomprising 2.4 mole percent total para-methylstyrene, including 1.05mole percent para-bromomethylstyrene, and having a Mooney viscosity of65 (1+8 min., 125° C.). The base terpolymer was dissolved by stirring atroom temperature overnight. A tetrabutylammonium salt of methacrylicacid was prepared in a second flask by charging 123.6 mLtetrabutylammonium hydroxide (1.0M in methanol) 9.6 mL methacrylic acid,1.02g 4-hydroxybenzophenone and 100 mL isopropanol (IPA) to the flaskand swirling the contents of the flask at room temperature, giving awater-white clear solution. This solution was then added to the flaskcontaining the dissolved base terpolymer, at a circulating bathtemperature of 83° C. After 45 minutes, the bath temperature was raisedto 95° C. and let to run for 7.5 h. Then the bath temperature waslowered to 70° C., and after a 2.5 h period, the reaction was let tocool. The yellowish viscous solution was quenched and washed with 10 mLHCl in 1000 mL distilled water, and subsequently washed with H₂ O/IPA(70:30) 5 to 6 times. The polymer was isolated by precipitation intoisopropanol and dried in vacuo for 48 h at 1 mm Hg and 80° C. Solutionviscosity of the recovered material was identical to the startingmaterial, and ¹ HNMR (400MH_(z), CDCl₃) analysis of the functionalizedpolymer indicated quantative conversion of the benzyl bromide. Theresults of NMR analysis show 0.83 mol % of methacrylate and 0.1 mol %benzophenone functionality in the polymer.

EXAMPLE B

This example shows the preparation of the sorbic acid, i.e.,2,4-hexadienoic acid, derivative ofisobutylene/para-methylstyrene/para-bromomethylstyrene terpolymer(SA-IPMS).

The process of Example A was repeated as set forth therein using thesame base terpolymer except that the charge to the second flask was 119mL of tetrabutylammonium hydroxide (1.0M in methanol), 12.3 g of sorbicacid, 2.04 g of 4-hydroxybenzophenone and 100 mL of isopropanol.

Solution viscosity of the recovered material was identical to thestarting material, and ¹ HNMR (400MH_(z), CDCl₃) analysis of thefunctionalized polymer indicated quantitative conversion of the benzylbromide. The results of NMR analysis show 0.77 mol % of sorbate and 0.2mol % of benzophenone.

EXAMPLE 1

Rubber Masterbatches (MB) were prepared by blending 100 parts by weightof MA-IPMS and 50 parts by weight of N-660 reinforcing grade carbonblack on a two roll mill at a temperature of 40° C. and for a period of10 minutes. This Masterbatch is designated MA-MB. A separate Masterbatchwas also prepared by blending 100 parts by weight of NR and 50 parts byweight of the carbon black in the same manner, and designated NR-MB.Portions of these Masterbatches were blended at the ratios set forth inruns B through G in Table 1. Then, 15 parts by weight of each blendedMasterbatch and control Masterbatches A and H were further compoundedwith the curatives set forth in the Table by mixing in a two roll millat a temperature of about 18° C. for a period of about 4 minutes. Allformulation quantities in Table 1 are parts by weight (PBW).

Curing behavior of these blends was then evaluated using a MonsantoOscillating Disk Rheometer at 160° C. --3 degree arc for 60 minutes. Theinitial ML and 60 min M_(H) values are reported in Table 1.

                                      TABLE 1                                     __________________________________________________________________________               A   B  C  D  E  F   G   H                                          __________________________________________________________________________    MA-MB      100 95 90 85 70 50  30  0                                          NR-MB      0   5  10 15 30 50  70  100                                        MASTER BATCH                                                                             15  15 15 15 15 15  15  15                                         (PBW)                                                                         ZnO        0.3 0.3                                                                              0.3                                                                              0.3                                                                              0.3                                                                              0.3 0.3 0.3                                        SULFUR     0.15                                                                              0.15                                                                             0.15                                                                             0.15                                                                             0.15                                                                             0.15                                                                              0.15                                                                              0.15                                       TMTDS      0.05                                                                              0.05                                                                             0.05                                                                             0.05                                                                             0.05                                                                             0.05                                                                              0.05                                                                              0.05                                       ETHYL ZIMITE                                                                             0.1 0.1                                                                              0.1                                                                              0.1                                                                              0.1                                                                              0.1 0.1 0.1                                        60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               ML (LB-IN) 39.06                                                                             32.35                                                                            34.81                                                                            26.43                                                                            17.88                                                                            12.65                                                                             4.34                                                                              3.84                                       MH (LB-IN) 63.11                                                                             70.61                                                                            91.71                                                                            91.48                                                                            90.51                                                                            86.54                                                                             60.21                                                                             43.82                                      MH-ML (LB-IN)                                                                            24.05                                                                             38.26                                                                            56.89                                                                            65.05                                                                            72.63                                                                            73.88                                                                             55.87                                                                             39.99                                      T.sub.s 2 (MIN)                                                                          2.91                                                                              1.19                                                                             1.09                                                                             1.06                                                                             1.12                                                                             1.11                                                                              1.01                                                                              1.32                                       T50 (MIN)  20.76                                                                             5.09                                                                             3.61                                                                             2.44                                                                             2.04                                                                             .85 1.60                                                                              1.84                                       T90 (MIN)  49.32                                                                             22.72                                                                            14.91                                                                            11.41                                                                            8.07                                                                             329 1.98                                                                              2.20                                       SLOPE @ T50                                                                              0.50                                                                              3.10                                                                             5.70                                                                             9.50                                                                             48.50                                                                            100.60                                                                            125.30                                                                            71.30                                      __________________________________________________________________________

Differential Rheometer values (MH minus ML) shown in Table 1 demonstratea remarkable and synergistic curing efficiency for the blended polymersas compared to the unblended polymers represented by samples A and H. Atall blend levels the curing efficiency consistently surpassed thetie-line values for purely intramolecular curing which would be expectedto range between the MH-ML value of 24.05 for the composition containingonly the ester functionalized isobutylene/para-methylstryrene terpolymer(A) and the MH-ML value of 39.99 for the composition containing onlynatural rubber (H) as elastomeric components. This phenomenon reflectsintermolecular (or cross) curing between the ester-modified copolymerphase and the natural rubber phase, in addition to the expectedintramolecular curing of these individual phases.

EXAMPLE 2 (Control)

Runs A through H of Example 1 were repeated in all respects and with thesame curatives as set forth in Example 1 except that the ester modifiedisobutylene/para-methylstyrene elastomer (MA-IPMS) was completelyreplaced with a non-halogenated copolymer of isobutylene and isopreneidentified above as Butyl 268.

Rheometer values for the various runs are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________              A   B   C  D   E  F   G  H                                          __________________________________________________________________________    BUTYL     100 95  90 80  70 50  30 0                                          268-MB                                                                        NR-MB     0   5   10 20  30 50  70 100                                        MASTER BATCH                                                                            15  15  15 15  15 15  15 15                                         (PBW)                                                                         Curatives (SAME AS EXAMPLE 1)                                                 60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               MH (LB-IN)                                                                              66.45                                                                             NT  23.03                                                                            29.98                                                                             34.61                                                                            47.17                                                                             51.33                                                                            42.42                                      ML (LB-IN)                                                                              13.57                                                                             NT  13.83                                                                            12.61                                                                             10.29                                                                            6.42                                                                              3.37                                                                             1.39                                       MH-ML (LB-IN)                                                                           52.88                                                                             NT  9.20                                                                             17.37                                                                             24.32                                                                            40.75                                                                             47.96                                                                            41.03                                      Ts2 (MIN) 2.16                                                                              NT  1.24                                                                             1.22                                                                              1.09                                                                             1.17                                                                              1.16                                                                             1.29                                       T50 (MIN) 7.11                                                                              NT  1.64                                                                             1.69                                                                              1.60                                                                             1.75                                                                              1.67                                                                             1.66                                       T90 (MIN) 24.52                                                                             NT  2.68                                                                             2.41                                                                              2.16                                                                             2.09                                                                              2.03                                                                             2.00                                       SLOPE @ 150                                                                             2.60                                                                              NT  6.40                                                                             14.10                                                                             30.90                                                                            26.79                                                                             NT 85.80                                      __________________________________________________________________________     NT  Not Tested                                                           

A comparison of the differential rheometer values (MH minus ML) showsthat at natural rubber levels below about 50% by weight there is amarked fall-off of curing efficiency well below the tie-line valueswhich range between 52.88 and 41.03 for the compositions containing onlyButyl 268 and natural rubber respectively. Rheometer values somewhatabove tie line are demonstrated for blends containing 50% by weight andgreater of natural rubber, probably due to natural rubber overcure atthese higher natural rubber levels.

The comparative differential Rheometer values for compositions preparedin Examples 1 and 2 are graphically illustrated in FIG. 1.

EXAMPLE 3

Example 1 was repeated in all respects as set forth therein except thatan elastomeric copolymer of butadiene and styrene, identified above asSBR-1502, was used as the diolefin copolymer component instead ofnatural rubber. Formulation and rheometry data are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________              A   B   C  D   E  F   G  H                                          __________________________________________________________________________    MA-MB     100 95  90 85  70 50  30 0                                          SBR-MB    0   5   10 15  30 50  70 100                                        MASTER BATCH                                                                            15  15  15 15  15 15  15 15                                         (PBW)                                                                         Curatives (SAME AS EXAMPLE 1)                                                 60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               ML (LB-IN)                                                                              37.19                                                                             37.65                                                                             31.03                                                                            22.72                                                                             19.79                                                                            17.73                                                                             14.19                                                                            7.79                                       MH (LB-IN)                                                                              62.74                                                                             68.59                                                                             70.26                                                                            66.35                                                                             84.86                                                                            101.39                                                                            96.20                                                                            92.48                                      MH-ML (LB-IN)                                                                           25.55                                                                             30.94                                                                             39.23                                                                            43.62                                                                             65.07                                                                            83.65                                                                             82.00                                                                            84.69                                      Ts2 (MIN) 4.46                                                                              1.19                                                                              1.21                                                                             1.24                                                                              1.25                                                                             1.34                                                                              1.48                                                                             1.51                                       T50 (MIN) 25.48                                                                             5.57                                                                              3.87                                                                             3.62                                                                              2.92                                                                             3.24                                                                              3.05                                                                             3.02                                       T90 (MIN) 49.98                                                                             26.82                                                                             22.48                                                                            20.58                                                                             23.55                                                                            27.37                                                                             15.12                                                                            5.82                                       SLOPE @ T50                                                                             0.60                                                                              1.40                                                                              2.50                                                                             3.10                                                                              9.40                                                                             9.70                                                                              30.90                                                                            42.40                                      __________________________________________________________________________

EXAMPLE 4

Example 3 was repeated in all respects as set forth therein except thatthe methyl acrylate ester copolymer used in Example 3 (MA-IPMS) wascompletely replaced with the sorbic acid ester copolymer defined aboveas SA-IPMS. Formulation and rheometry data are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________              A   B   C  D   E  F   G  H                                          __________________________________________________________________________    SA-MB     100 95  90 85  70 50  30 0                                          SBR-MB    0   5   10 15  30 50  70 100                                        MASTER BATCH                                                                            15  15  15 15  15 15  15 15                                         (PBW)                                                                         Curatives (SAME AS EXAMPLE 1)                                                 60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               MH (LB-IN)                                                                              31.25                                                                             29.00                                                                             26.20                                                                            23.56                                                                             19.04                                                                            16.87                                                                             13.19                                                                            7.79                                       ML (LB-IN)                                                                              55.18                                                                             52.60                                                                             64.78                                                                            70.28                                                                             77.36                                                                            94.68                                                                             88.55                                                                            92.48                                      MH-ML (LB-IN)                                                                           23.93                                                                             23.60                                                                             38.57                                                                            46.72                                                                             58.32                                                                            77.80                                                                             75.36                                                                            84.69                                      Ts2 (MIN) 3.70                                                                              2.18                                                                              1.61                                                                             1.49                                                                              1.42                                                                             1.42                                                                              1.54                                                                             1.51                                       T50 (MIN) 21.51                                                                             8.21                                                                              8.17                                                                             7.49                                                                              4.38                                                                             3.43                                                                              3.06                                                                             3.02                                       T90 (MIN) 51.69                                                                             34.69                                                                             29.35                                                                            27.50                                                                             24.17                                                                            20.35                                                                             12.28                                                                            5.82                                       SLOPE @ T50                                                                             0.30                                                                              0.90                                                                              1.40                                                                             1.80                                                                              3.50                                                                             10.80                                                                             30.30                                                                            42.40                                      __________________________________________________________________________

As is graphically shown in FIG. 2, the differential rheometer torquevalues achieved in the compositions of Examples 3 and 4 consistentlyexceed the expected tie line values, except for an anomalous result of23.60 in formulation B of Example 4. This is indicative of enhancedvulcanization efficiency due to the presence intermolecular as well asintramolecular crosslinking.

EXAMPLE 5

Example 1 was repeated in all respects as set forth therein except thatthe methyl acrylate ester used in Example 1 (MA-IPMS) was completelyreplaced with the sorbic acid ester identified above as SA-IPMS.Formulation and rheometry data are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________              A   B  C   D  E   F  G   H                                          __________________________________________________________________________    SA-MB     100 95 90  85 70  50 30  0                                          NR-MB     0   5  10  15 30  50 70  100                                        MASTERBATCH                                                                             15  15 15  15 15  15 15  15                                         (PBW)                                                                         CURATIVES (SAME AS EXAMPLE 1)                                                 60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               ML (LB-IN)                                                                              24.05                                                                             26.29                                                                            24.88                                                                             23.19                                                                            18.49                                                                             10.88                                                                            6.81                                                                              1.39                                       MH (LB-IN)                                                                              48.37                                                                             57.62                                                                            68.87                                                                             72.03                                                                            71.55                                                                             68.69                                                                            60.81                                                                             42.42                                      MH-ML (LB-IN)                                                                           24.32                                                                             31.33                                                                            44.00                                                                             48.84                                                                            53.06                                                                             57.81                                                                            54.00                                                                             41.03                                      Ts2 (MIN) 3.00                                                                              1.46                                                                             1.40                                                                              1.24                                                                             1.52                                                                              1.19                                                                             1.21                                                                              1.29                                       T50 (MIN) 16.10                                                                             4.73                                                                             4.16                                                                              3.46                                                                             2.93                                                                              1.96                                                                             1.84                                                                              1.66                                       T90 (MIN) 48.34                                                                             16.80                                                                            18.02                                                                             16.21                                                                            16.64                                                                             11.35                                                                            2.23                                                                              2.00                                       SLOPE @ T50                                                                             0.50                                                                              2.60                                                                             4.10                                                                              5.80                                                                             10.30                                                                             71.50                                                                            115.30                                                                            85.80                                      __________________________________________________________________________

Once again, differential rheometer values are consistently above thetie-line values.

EXAMPLE 6

Example 1 was repeated as set forth therein except that the naturalrubber component of the blend was replaced completely by a syntheticpolyisoprene identified above as NATSYN 2200.

                                      TABLE 6                                     __________________________________________________________________________              A   B  C   D  E   F  G   H                                          __________________________________________________________________________    MA-MB     100 95 90  85 70  50 30  0                                          PI-MB     0   5  10  15 30  50 70  100                                        MASTERBATCH                                                                             15  15 15  15 15  15 15  15                                         (PBW)                                                                         CURATIVES (SAME AS EXAMPLE 1)                                                 60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               ML (LB-IN)                                                                              39.06                                                                             32.73                                                                            34.35                                                                             30.19                                                                            14.04                                                                             7.24                                                                             2.82                                                                              1.22                                       MH (LB-IN)                                                                              63.11                                                                             65.82                                                                            76.70                                                                             91.58                                                                            88.21                                                                             77.02                                                                            64.65                                                                             48.08                                      MH-ML (LB-IN)                                                                           24.05                                                                             33.09                                                                            42.35                                                                             61.39                                                                            74.17                                                                             69.78                                                                            61.83                                                                             46.85                                      Ts2 (MIN) 2.91                                                                              1.18                                                                             1.70                                                                              0.99                                                                             0.97                                                                              1.07                                                                             1.15                                                                              1.24                                       T50 (MIN) 20.76                                                                             6.59                                                                             6.09                                                                              2.60                                                                             1.76                                                                              1.84                                                                             1.82                                                                              1.87                                       T90 (MIN) 49.32                                                                             38.13                                                                            34.95                                                                             14.71                                                                            6.05                                                                              2.33                                                                             2.14                                                                              2.12                                       SLOPE @ T50                                                                             0.50                                                                              1.40                                                                             1.50                                                                              6.00                                                                             61.50                                                                             86.80                                                                            122.50                                                                            104.60                                     __________________________________________________________________________

The data in Table 6 shows increased curing efficiency above tie-linevalues at all blend levels.

The following example illustrates the use of a peroxide cure system forpreparing the covulcanizates of this invention.

EXAMPLE 7

Example 6 was repeated as set forth above except that the ZnO, sulfur,TMTDA and Ethyl Zimate curing system was eliminated and replaced withdicumylperoxide used at a level of 2% by weight per hundred parts ofrubber (pHR). Formulation and rheometry data are shown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________              A   B  C   D  E   F  G   H                                          __________________________________________________________________________    MA-MB     100 95 90  85 70  50 30  0                                          PI-MB     0   5  10  15 30  50 70  100                                        MASTERBATCH                                                                             15  15 15  15 15  15 15  15                                         (PBW)                                                                         Di-CUMYL  0.2 0.2                                                                              0.2 0.2                                                                              0.2 0.2                                                                              0.2 0.2                                        PEROXIDE                                                                      60 MIN. RHEOMETERS AT 160° C./3 DEG. ARC                               ML (LB-IN)                                                                              15.80                                                                             22.90                                                                            21.98                                                                             16.23                                                                            12.01                                                                             8.43                                                                             5.27                                                                              2.03                                       MH (LB-IN)                                                                              51.01                                                                             49.04                                                                            51.42                                                                             51.17                                                                            48.46                                                                             49.94                                                                            42.75                                                                             39.34                                      MH-ML (LB-IN)                                                                           35.45                                                                             26.14                                                                            29.44                                                                             34.94                                                                            36.45                                                                             41.51                                                                            37.48                                                                             37.30                                      Ts2 (MIN) 1.66                                                                              1.76                                                                             1.63                                                                              1.60                                                                             1.57                                                                              1.39                                                                             1.54                                                                              1.29                                       T50 (MIN) 3.29                                                                              3.49                                                                             3.46                                                                              3.62                                                                             3.85                                                                              3.77                                                                             4.25                                                                              3.98                                       T90 (MIN) 6.76                                                                              8.38                                                                             8.33                                                                              8.35                                                                             8.43                                                                              8.43                                                                             9.48                                                                              8.84                                       SLOPE @ T50                                                                             8.80                                                                              5.10                                                                             5.70                                                                              6.40                                                                             6.20                                                                              6.90                                                                             5.50                                                                              5.60                                       __________________________________________________________________________

The data in Table 7 shows increased curing efficiency above tie-linevalues at blend levels of polyisoprene above about 30% by weight.

EXAMPLE 8

In this example, a series of rubber formulations were prepared, curedand physical properties were evaluated. The composition of theseformulations (parts by weight), curing conditions and physical propertydata is shown in Table 8. The elastomer identified as XP-50 is anon-halogenated random copolymer of isobutylene and para-methylstyrene(PMS) having a PMS content of about 5.0 wt %; the elastomer identifiedas BZMA is a methacrylic acid derivative of anisobutylene/para-methylstyrene/para-bromomethylstyrene terpolymerprepared as in Example A, but having a content of about 0.7 mole %methacrylate and 0.1 mole % benzophenone; the elastomer identified asBZMA-1 is similar to BZMA except that is has a methacrylate content ofabout 0.35 mole %; NR is natural rubber and PI is synthetic polyisopreneas disclosed above.

Formulations A, B and C of Table 8 are formulations containing anon-functionalized isobutylene/para-methylstyrene copolymer which areoutside the scope of this invention. No intervulcanization betweendifferent polymer molecules takes place under curing conditions using asulfur curing system.

Formulations D, E and F of Table 8 are formulations within the inventioncured with a sulfur curing system and formulations G, H and I areformulations within the invention cured using a peroxide system(di-cumyl peroxide).

Achievement of a truly intervulcanized composition is reflected byenhanced tensile and elongation properties for formulations D through Ias compared with formulations A through C, where no intermolecularcrosslinking takes place during the vulcanization process.

                                      TABLE 8                                     __________________________________________________________________________                  A   B   C   D   E   F   G   H   I                               __________________________________________________________________________    NR            30  50  70  30  50  70  --  --  --                              XP-50         70  50  30  --  --  --  --  --  --                              PI            --  --  --  --  --  --  30  50  70                              BZMA          --  --  --  70  50  30  --  --  --                              BZMA-1        --  --  --  --  --  --  70  50  30                              CAR. BLK      50  50  50  50  50  50  50  50  50                              ZnO           2   2   2   2   2   2   --  --  --                              Sulfur        1   1   1   1   1   1   --  --  --                              TMTDS         0.3 0.3 0.3 0.3 0.3 0.3 --  --  --                              ETHYL ZIMATE  0.7 0.7 0.7 0.7 0.7 0.7 --  --  --                              DICUP 40 KE   --  --  --  --  --  --  4   4   4                               CURE TIME (MIN)                                                                             20  10  10  30  30  20  12  12  12                              CURE TEMP (°C.)                                                                      160 160 160 160 160 160 170 170 170                             PHYSICAL PROPERTIES                                                           SHORE A HARDNESS                                                                            64.9                                                                              62.3                                                                              58.9                                                                              61.5                                                                              58  53.5                                                                              54.9                                                                              52.3                                                                              52.1                            TENSILE @ 100% MPA                                                                          2.42                                                                              2.52                                                                              2.01                                                                              3.29                                                                              2.5 2.0 2.1 2.0 1.65                            TENSILE @ 200% MPA                                                                          3.43                                                                              5.5 4.88                                                                              9.55                                                                              6.94                                                                              5.0 6.5 6.5 5.38                            TENSILE @ 300% MPA                                                                          --  7.84                                                                              8.73                                                                              --  --  10.02                                                                             11.52                                                                             11.47                                                                             10.71                           TENSILE @ BREAK MPA                                                                         3.47                                                                              8.13                                                                              13.66                                                                             11.55                                                                             10.63                                                                             17.59                                                                             13.37                                                                             15.4                                                                              16.83                           ELONGATION @ BREAK                                                                          207 332 437 217 263 453 336 373 415                             TEAR DIE B Kn/M2                                                                            24.89                                                                             27.78                                                                             25.3                                                                              --  --  --  19.3                                                                              20.6                                                                              17.6                            __________________________________________________________________________

What is claimed is:
 1. A composition vulcanizable by free-radicalvulcanization comprising a mixture of:a) an ethylene propylene dieneterpolymer elastomer having a number average molecular weight of atleast 10,000 and containing from about 0.01 up to about 10 mole % Yfunctional groups randomly along and pendant to the elastomeric polymerchain, said Y functional groups containing a substituent group and anolefinic or vinyl double bond alpha, beta to the substituent group, saidsubstituent group selected from the group consisting of carbonyl,phosphoryl, sulfonyl, nitrile, and aromatic ring-containing group, thesubstituent group being capable of activation said double bond towardsfree radical addition reactions; and b) a diolefin homopolymer orcopolymer rubber;the weight ratio of said elastomeric copolymer anddiolefin homopolymer or copolymer rubber present in said mixture beingwithin the range of about 1:99 to 99:1.
 2. The composition of claim 1wherein said elastomer copolymer is a terpolymer of ethylene, propyleneand up to about 10 wt % of a non-conjugated diene.
 3. The composition ofclaim 2 wherein said substituent group is a carbonyl-containing group.4. The composition of claim 3 wherein said Y functional group is anester group represented by the structure. ##STR6## wherein R₂ and R₃ areindependently selected from the group consisting of hydrogen and analkyl group containing 1 to about 6 carbon atoms and R₄ is selected fromthe group consisting of hydrogen, an alkyl group containing from 1 toabout 28 carbon atoms, an aryl group and an alkenyl group containingfrom 2 to about carbon atoms.
 5. The composition of claim 4 containingfrom about 0.05 to about 2.0 mole % of said Y ester groups.
 6. Thecomposition of claim 1 wherein said diolefin homopolymer or copolymerrubber comprises an elastomer selected from the group consisting ofpolybutadiene, copolymers of butadiene with styrene or acrylonitrile,natural rubber, polychloroprene, polyisoprene, copolymers of ethylene,propylene and up to 10 wt % of a non-conjugated diene, copolymers ofisobutylene and up to 10 wt % of isoprene, mixtures thereof.
 7. Thecomposition of claim 1 further containing an accelerated sulfur curingsystem.
 8. The composition of claim 7 further containing Zinc oxide. 9.The composition of claim 1 further containing a peroxide curing system.10. The composition of claim 1 further containing a reinforcing filler.11. A process for preparing an intervulcanized elastomer compositioncomprising:i) forming the mixture as defined in claim 1; and ii)subjecting said mixture to free-radical curing conditions for a periodof time sufficient to vulcanize said composition.
 12. The process ofclaim 11 wherein said free radical curing conditions include heatingsaid composition to a temperature in the range of from about 100° C. toabout 180° C.
 13. The process of claim 12 wherein said compositioncontains an accelerated sulfur curing system.
 14. The process of claim12 wherein said composition contains a peroxide curing system.
 15. Theprocess of claim 12 wherein said temperature ranges from about 120° C.to about 160° C.
 16. An intervulcanized composition produced by theprocess of claim
 11. 17. The vulcanized composition obtained from thevulcanization of the composition of claim 1 characterized by a maximumrheometer torque increase ratio in accordance with the formula:ΔM_(a+b)/(ΔM_(a) f_(a) +ΔM_(b) f_(b)) of greater than 1.25, wherein:ΔM_(a+b)=the torque increase observed for the blend of polymer (a) and polymer(b); ΔM_(a) =the torque increase observed for polymer (a) on its own;f_(a) =the weight fraction of polymer (a) in the blend; ΔM_(b) =thetorque increase observed for polymer (b) on its own; and f_(b) =theweight fraction of polymer (b) in the blend.
 18. The composition ofclaim 17 wherein said rheometer torque is measured using an oscillatingdisc rheometer, cure time 60 minutes at 160° C. and 3° arc.
 19. Thecomposition of claim 17 wherein said torque increase ratio is greaterthan 1.5.
 20. The composition of claim 17 wherein said torque increaseratio is greater than 2.0.
 21. An intervulcanized composition of a blendof elastomers, said intervulcanized blend comprising a diolefinhomopolymer or copolymer rubber and an ethylene propylene dieneterpolymer having covalently bonded along the polymer backbone Y groupscontaining a free olefinic or vinyl double bond positioned alpha, betato a substituent group which activates the double bond for free radicaladdition reactions in the presence of a free radical generator, saidsubstituent group selected from the group consisting of carbonyl,phosphoryl, sulfonyl, nitrile, and aromatic ring-containing groups. 22.The composition of claim 21 wherein said Y group is an ester grouprepresented by the structure: ##STR7## wherein R₂ and R₃ areindependently selected from the group consisting of hydrogen and analkyl group containing 1 to about 6 carbon atoms and R₄ is selected fromthe group consisting of hydrogen, an alkyl group containing from 1 toabout 28 carbon atoms, an aryl group and an alkenyl group containingfrom 2 to about 28 carbon atoms.
 23. The composition of claim 22containing from about 0.05 to about 2.0 mole % of said Y ester groups.24. The composition of claim 21 wherein said diolefin homopolymer orcopolymer rubber comprises an elastomer selected from the groupconsisting of polybutadiene, copolymers of butadiene with styrene oracrylonitrile, natural rubber, polychloroprene, polyisoprene, copolymersof ethylene, propylene and up to 10 wt % of a non-conjugated diene,copolymers of isobutylene and up to 10 wt % of isoprene, and mixturesthereof.
 25. The composition of claim 21 further containing areinforcing filler.
 26. The composition of claim 22 where R₂ is methyland R₃ and R₄ are each hydrogen.
 27. The composition of claim 22 whereR₂, R₃ and R₄ are each hydrogen.
 28. The composition of claim 22 whereR₂ and R₃ are each hydrogen and R₄ is C₄ alkenyl.